1. Technical Field
The present invention relates to an apparatus that prevents battery overcharge by detecting cell expansion even with a minimal amount of generated gas when a cell swells due to battery overcharge and accordingly disconnects a charging circuit to ensure the stability of a battery.
2. Description of the Related Art
Recently, as a solution for environmental pollution caused by fossil fuel, environmentally-friendly vehicles that utilize electricity as a main power source such as electric vehicles and hybrid vehicles is being developed. Environmentally-friendly vehicles require a battery to store electric energy, and especially a high-power and large-capacity battery to drive vehicles. Therefore, medium or large-sized batteries are usually employed. Since such medium or large-sized batteries are not easily mounted within vehicles due to their size and increase weight of vehicles, research into smaller batteries has been developed.
Recently, a battery structure employing a pouch meets the requirement and is drawing interest. Although batteries employing a pouch are advantageous in terms of electric efficiency, they have substantially low stability. Therefore, a technology is needed to obtain stability of the battery. In other words, in a battery employing a battery pack, when the battery is overcharged, voltage increases and overheat may occur, such that the battery cell swells due to gas generated therein. Accordingly, an overcharge safety apparatus is needed for high-voltage battery systems. The overcharge safety apparatus may protect a battery system from a fire by interrupting current flow to prevent thermal runaway when a battery is overcharged. In a passive type overcharge safety structure according to the prior art, expansion force occurring when a cell swells is utilized. When a cell swells sufficiently, cell expansion is caused by the opening of the end plate thus, breaking the cell tab part. Accordingly, current is interrupted and thus safety is ensured.
In the above structure, however, a cell must swell sufficiently before thermal runaway occurs. When a cell fails to swell sufficiently before thermal runaway, the apparatus operates with thermal runaway, and a fire may occur due to the thermal runaway even when current is interrupted. In addition, when the amount of the generated gas in a cell is insufficient, the cell tab part may not be broken.
As an alternative method for preventing battery overcharge, on the other hand, there is an active type technology that actively interrupts a relay. Such active type overcharge prevention structure includes sensors or switches to detect cell expansion and interrupts supplying power to a relay when cell expansion is detected and in turn current flow in a battery system. However, the technology to interrupt supplying power to a relay fails to interrupt current flow when the relay is fused. Additionally, the active type overcharge safety structure does not ensure safety when electric components such as sensors and switches fail in emergency situations such as accidents causing the components to not be operable. The matters described as the related art have been provided merely for facilitating the understanding of the background of the present invention and should not be construed as acknowledging them as the prior art already known to those skilled in the art.